Ari T. Friberg

Characterization of polarization fluctuations in random electromagnetic beams

Two stationary, partially polarized electromagnetic beams with equal degrees of polarization may exhibit completely different time evolutions of the instantaneous polarization state. In this work, we derive a statistical quantity that describes the rate at which the field intensity in the beam, on average, is redistributed between the beams polarization state at any time and the state orthogonal to it. This method allows one to treat the dynamical properties of the polarization fluctuations both theoretically and experimentally. We demonstrate the method by applying it to important special cases, such as fields obeying Gaussian statistics, black-body radiation pencils and depolarized laser beams. We also prove that a geometric approach introduced earlier is closely connected with the present model.

Conoscopic interferometry of wafers for surface-acoustic wave devices

We show that in interpreting the conoscopic interference fringes, one should exercise care in employing approximate expressions which fail for certain crystal cuts. In this paper, we study 64°- and 128°-rotated Y-cut and Z-cut LiNbO3 wafers. We show that the error made in using the approximate formulae for the samples is more than 25% and that one has to use exact formulae in order to attain quantitative agreement with the experimental data.

Polarization time of unpolarized light

Light produced by most natural and artificial sources is unpolarized or partially polarized. At any instant of time, however, such random light can be regarded as fully polarized, but the polarization state may vary drastically within short time intervals. This rate of change is another attribute that separates one unpolarized beam from another. Here, we study such polarization dynamics and, for the first time to our knowledge, measure the characteristic time, called the polarization time, in which the instantaneous polarization state stays essentially unaltered. The technique employs a polarization-sensitive Michelson interferometer and two-photon absorption detection valid for electromagnetic light, yielding superior femtosecond time resolution. We analyze two unpolarized light sources: amplified spontaneous emission from a fiber amplifier and a dual-wavelength laser source. The characterization of polarization dynamics can have significant applications in optical sensing, polarimetry, telecommunication, and astronomy, as well as in quantum and atom optics.

Classical spectral ghost ellipsometry.

We introduce a novel ghost reflection ellipsometer for a spectral characterization of homogeneous thin films and interfaces. The device makes use of a uniform, spatially incoherent, unpolarized light source with Gaussian statistics and of the detection of intensity correlations. Unlike traditional ellipsometers, no source or detector calibration and reference sample are needed. The method is also insensitive to instrumentation errors. The ellipsometer that we present here is a classical analog of a quantum twin-photon arrangement discussed earlier in the literature. However, the classical configuration is easier to implement and use, because entangled photon pairs are not needed and appropriate light sources and detectors are readily available.

Generation and electromagnetic coherence of unpolarized three-component light fields.

Conditions for controlled generation of completely unpolarized, genuine three-component random light fields, both radiating and evanescent, in multi-beam illumination at a planar dielectric interface are explored. The associated electromagnetic degrees of coherence are also analyzed. Our results reveal the possibility to tailor fields with polarization properties identical to those of universal blackbody radiation, yet with tunable spatial coherence characteristics. Such unconventional, fully unpolarized three-component electromagnetic fields, not addressable by the traditional beam-field formalism, could be exploited in surface-photonic light-matter interactions.